Mercaptoalcohol corrosion inhibitors

ABSTRACT

Compositions and methods have been discovered for inhibiting corrosion of metals, particularly iron alloys, in contact with fluids, either hydrocarbons, alcohols, or aqueous fluids, employing mercaptoalcohols. The mercaptoalcohols should have at least one water solubilizing hydroxyl group. In particular, suitable mercaptoalcohols have the formula: 
     
       
         (HS) n —R—)(OH) m   
       
     
     where R is a straight, branched, cyclic or heterocyclic alkylene, arylene, alkylarylene, arylalkylene, or hydrocarbon moiety having from 1 to 30 carbon atoms; n and m each independently averages from 1 to 3; and the heteroatom in the heterocyclic moiety substituent, if present, may be N, O, S and/or P. Preferred mercaptoalcohols include 2-mercaptoethanol, 2-mercaptopropanol, 1-mercapto-2-propanol, and 2-mercaptobutanol, in part because they are soluble in many fluids. These corrosion inhibitors show improved inhibition of both generalized and localized corrosion, specifically in high shear and high flow environments.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/636,095, filed Aug. 10, 2000, that issued as U.S. Pat. No. 6,365,067B1 on Apr. 2, 2002 which claims benefit of 60/148,600, Aug. 12, 1999.

FIELD OF THE INVENTION

The present invention relates to methods and compositions for inhibitingcorrosion, and more particularly relates, in one embodiment, to methodsand compositions for inhibiting corrosion employing mercaptoalcohols.

BACKGROUND OF THE INVENTION

It is well known that steel tubulars and equipment used in theproduction of oil and gas are exposed to corrosive environments. Suchenvironments generally contain acid gases (CO₂ and H₂S) and brines ofvarious salinities. Under such conditions the steel will corrode,possibly leading to equipment failures, injuries, environmental damageand economic loss. Further in some cases, drilling fluids have acidintentionally added thereto in order to acidize the formations toenhance hydrocarbon recovering. This added acid also causes corrosionproblems.

While the rate at which corrosion will occur depends on a number offactors such as metallurgy, chemical nature of the corrosive agent,salinity, pH, temperature, flow rate, etc., some sort of corrosionalmost inevitably occurs. One way to mitigate this problem consists ofusing corrosion inhibitors in the hydrocarbon production system.

It is known in the art that the corrosion of iron and iron-based alloyssuch as steel alloys in contact with oil-in-brine emulsions can beinhibited by treating the emulsions with oil soluble, water soluble orwater-dispersible nitrogen-containing, phosphorus-containing and/orsulfur-containing corrosion inhibitors. Not all corrosion inhibitorsperform acceptably in all applications, e.g. severe applications such ashigh shear and high flow rate environments. Current technology for highshear/high flow applications also includes mercaptocarboxylic acid (e.g.mercaptoacetic acid) used with other conventional corrosion inhibitors(e.g. imidazolines).

Broad statements like those in U.S. Pat. No. 3,462,496 thatmercaptoalcohols are known to be useful as corrosion inhibitors are nothelpful in directing one having ordinary skill in the art to choosingwhich compositions would be effective as corrosion inhibitors inparticular applications. For instance, one of ordinary skill in the artwould not know which compounds would be useful in protecting copper orsteel or other iron alloys in contact with aqueous or hydrocarbonenvironments over particular temperature or pressure ranges, and thelike, based only upon such very sparse teachings. The minimalinstruction of U.S. Pat. No. 3,462,496 also does not teach theimportance that the mercaptoalcohols should be water soluble in certainenvironments.

It would be advantageous if a new corrosion inhibitor were discoveredthat would be an improvement over the presently known systems.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide acorrosion inhibitor composition that is effective in inhibiting thecorrosion of steel surfaces in oil field tubing and equipment,particularly both general and localized corrosion.

It is another object of the present invention to provide a water-solublecorrosion inhibitor that has relatively poor chelation of and lowersolubility of iron complexes, as well as increased film persistence.

In carrying out these and other objects of the invention, there isprovided, in one form, a corrosion inhibitor composition having at leastone mercaptoalcohol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a graph of corrosion inhibition (%) measured by linearpolarization resistance (LPR) for seven different sulfur-containingcorrosion inhibitor candidates and an imidazoline reference material asa function of concentration;

FIG. 1b is a graph of corrosion inhibition (%) measured by weight lossfor the seven different sulfur-containing corrosion inhibitor candidatesand the imidazoline reference material of FIG. 1a as a function ofconcentration;

FIG. 1c is a graph of corrosion inhibition (%) measured by iron countfor the seven different sulfur-containing corrosion inhibitor candidatesand the imidazoline reference material of FIG. 1a as a function ofconcentration;

FIG. 2 is a graph of corrosion inhibition (%) measured by LPR, weightloss, and iron count from FIGS. 1a-1 c for the seven best-performingsulfur-containing corrosion inhibitor candidates at a concentration of1.0 ppm;

FIG. 3 is a graph of corrosion inhibition (%) measured by LPR, weightloss, and iron count for 2ME, DTDPA, and TGA in brine at a concentrationof 1.0 ppm; and

FIG. 4 is a graph of corrosion inhibition (%) measured for 2ME and1-mercapto-2-propanol under identical conditions.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that corrosion inhibition, particularlyinhibition of localized corrosion (i.e. a high level of protection), aswell as generalized corrosion, is improved using mercaptoalcohols.Additionally, the mercaptoalcohols have relatively poor chelation of andrelatively lower solubility of iron complexes, and thus are unlikely tochelate/dissolve the surface iron of the metal structure that is beingprotected, as compared with other sulfur-containing corrosion inhibitors(e.g. thioglycolic acid). Further, it is believed that corrosioninhibitors containing the mercaptoalcohols of this invention haveincreased film persistency on the surface of the iron or steel or othersurface being protected (e.g. through disulfide formation, in anon-limiting example).

The corrosion inhibitors of the invention are suitable to protect ironand iron-based alloys, such as steel alloys, used in connection with oiland gas production, as well as in other corrosive environments.Corrosion inhibition of mild steel is preferred in one non-limitingembodiment. Particular non-limiting environments suitable for theinventive corrosion inhibitors include downhole and flowline multiplephase oilfield applications. The inventive compounds are expected tofind utility as corrosion inhibitors in the production or processing ofhydrocarbon products, such as petroleum and natural gas, e.g. Thecorrosion inhibitors of the invention are expected to have particularuse in high shear and high flow applications, although the invention iscertainly not limited to such environments and will find use in othercorrosive environments. High shear/high flow applications are simplysome of the most severe environments for corrosion inhibitors. It isexpected that if a corrosion inhibitor works well in such environments,it will work well under milder conditions. It is further preferred, in anon-limiting embodiment, to use the inventive corrosion inhibitors incontinuous flow applications, although they could be used in stagnantenvironments. Further, it is expected that the mercaptoalcohols of thisinvention would be useful across broad temperature and pressure ranges.

The corrosion inhibitors useful in this invention include, but are notnecessarily limited to, simple mercaptoalcohols. In particular, suitablemercaptoalcohols have the formula:

(HS)_(n)—R—(OH)_(m)

where R is a straight, branched, cyclic or heterocyclic alkylene,arylene, alkylarylene, arylalkylene, or hydrocarbon moiety having from 1to 30 carbon atoms, and n and m each independently average from 1 to 3.The heteroatoms in the heterocyclic moiety substituent may be N, O, Sand/or P. Preferably, R has from 1 to about 24 carbon atoms, and naverages from 1 to 2. In another non-limiting, preferred embodiment, Ris a straight chain hydrocarbon moiety having from 1 to 8 carbon atoms,n is 1 and m is 1 to 2; most preferably, R is an alkylene group and m isalso 1. In still another non-limiting embodiment, R has from 1 to 6carbon atoms, preferably 1 to 5 carbon atoms, and most preferably 1 to 4carbon atoms.

In a preferred, non-limiting embodiment, the mercaptoalcohol is a watersoluble mercaptoalcohol having the formula:

where R′ and R″ are independently selected from the group consisting ofH, straight, branched, cyclic or heterocyclic, alkyl, aryl, alkylaryland arylalkyl where the heteroatom in the heterocyclic moiety isselected from the group consisting of N, O, S and P, and where the totalnumber of carbon atoms in the mercaptoalcohol is from 1 to 8.

In one non-limiting preferred embodiment, the mercaptoalcohol is2-mercaptoethanol (2ME), 2-mercaptopropanol (2MP), 1-mercapto-2-propanol(MP), and/or 2-mercaptobutanol (2MB) or mixtures thereof. These lowmolecular weight mercaptoalcohols are preferred because of their widerange of solubility. For instance, 2ME is soluble in water, alcohols andhydrocarbons, and thus can serve as a corrosion inhibitor for ironalloys in contact with a wide variety of fluids. In one non-limitingembodiment of the invention, the only corrosion inhibitor used is amercaptoalcohol, more specifically one of either of the above formuladefinitions, and preferably one or more from the four-member group of2ME, 2MP, MP and/or 2MB. In another embodiment, the only corrosioninhibitor employed is 2ME.

In general, solubility of the mercaptoalcohols of this invention can beimproved by lowering the number of carbons in R. Solubility in aqueoussolutions can also be increased by increasing the number of hydroxylgroups. For example, if the mercaptoalcohol has a relatively largenumber of carbon atoms in the R moiety, its solubility in aqueoussolutions may be increased by having two or three hydroxyl substituents.

Additional corrosion inhibitors may also be optionally used inconjunction with the mercaptoalcohols. More specifically, such suitableadditional corrosion inhibitors include, but are not necessarily limitedto, imidazolines, amides, amines, quaternary amines, phosphate esters,polycarboxylic acids, thiols, disulfides and other sulfur-containingcompounds and mixtures thereof. Nitrogen-containing corrosion inhibitorsare preferred in one non-limiting embodiment of the invention. There issome evidence that nitrogen-containing corrosion inhibitors togetherwith mercaptoalcohols may give a synergistic effect over the use ofeither type of corrosion inhibitor alone.

In the inventive corrosion inhibiting compositions, the proportion ofmercaptoalcohol in the composition may range from about 0.1 to about 70wt. %. Preferably, the proportion of mercaptoalcohol in the compositionranges from about 1 to about 40 wt. %.

Solvents or diluents may be employed together with the composition ofthis invention, which solvents may include, but are not necessarilylimited to, water, alcohols, aromatic solvents, such as naphthas andxylene, and the like. It is important that the mercaptoalcohols of theinvention be water-soluble so that they can be transported to and form afilm on the metal surface initially in contact with thehydrocarbon/water mixture.

It will be appreciated that the inventive corrosion inhibitingcomposition of the invention can be used in any fluid (hydrocarbon-basedor aqueous-based) contacting metal. By “hydrocarbon” is meant any crudeoil; refined hydrocarbon; emulsion of oil-in-water or water-in-oil;whether recovered from a hydrocarbon recovery operation, used to assistwith a hydrocarbon recovery operation, such as a hydrocarbon-containingdrilling fluid or drill-in fluid (DIF), workover fluid, completionfluid, or the like; or produced as a by-product or waste product from ahydrocarbon refining or processing operation whether or not in emulsionform, or the like. The inventive corrosion inhibiting composition of theinvention can be also used in any aqueous fluid, such as brine in onenon-limiting example. Additionally, the inventive corrosion inhibitingcomposition can be used to inhibit corrosion that may occur in alcoholsor alcohol-based fluids.

It is difficult, if not impossible, to specify with precision the amountof composition of this invention that would be suitable to add to thehydrocarbon to impart corrosion inhibition properties thereto. Such aneffective amount depends on a number of factors, including, but notnecessarily limited to, the nature of the hydrocarbon, the exactcomposition of the corrosion inhibitor (the nature of the components andtheir proportion), the properties of the hydrocarbon or fluid (e.g.temperature, pressure, pH, composition, contaminants, etc.), flow rates,and the like. However, in one non-limiting embodiment, the amount ofcomposition added to a hydrocarbon to be effective may range from about1 to about 1,000 ppm, based on the hydrocarbon, preferably from about 10to about 100 ppm.

The invention will be further illustrated by the following examples thatare merely intended to further demonstrate, but not limit, theinvention.

EXAMPLE 1

Initial sparged beaker (SB) and rotating cylinder electrode (RCE) testswere performed with 2-mercaptoethanol (2ME) by itself and in formulationwith nitrogen-containing compounds (i.e. imidazoline). The resultsshowed strong corrosion inhibition of mild steel under typical oilfieldconditions: >98% inhibition at 5 ppm concentration.

EXAMPLE 2

A water-soluble mercaptoalcohol corrosion inhibitor, specifically2-mercaptoethanol (2ME) was added at 1 ppm in a CO₂-saturated mixture ofbrine and oil (volume proportion of 80:20) at 160° F. (71° C.) and 1 atm(101 mPa) and the corrosion rate was measured by linear polarizationresistance (LPR), weight loss, and iron count methods. The addition of2-mercaptoethanol resulted in a corrosion inhibition of 98% compared to89% when conventional mercaptoacetic acid was used at the samepercentage in the formulation.

EXAMPLE 3

The following seven sulfur-containing corrosion inhibition candidateswere tested for corrosion inhibition using LPR, weight loss and ironcount methods at various concentrations at the conditions shown at thetop of FIG. 1a:

Thioglycolic acid (TGA) 3,3′-Dithiodipropionic acid (DTDPA) Thiosulfate(ST) Thiourea (TH) 2-Mercaptoethanol (2ME) L-Cysteine (L-CY) tert-Butylmercaptan (t-BM)

The LPR data is plotted in FIG. 1a; the weight loss data is plotted inFIG. 1b; and the iron count data is plotted in FIG. 1c. The seven topperforming candidates had their corrosion inhibition values charted at1.0 ppm in FIG. 2. 2ME was the only candidate where the corrosioninhibition values were consistently better than 95%. Animidazoline-based product (IM) was used as a reference.

EXAMPLE 4

A sparged beaker (SB) test using an aqueous, non-hydrocarbon, e.g. brinewas conducted using the conditions outlined at the top of FIG. 3 using2ME of the invention and comparative DTDPA and TGA. Corrosion wasmeasured using LPR, weight loss, and iron count methods. As shown inFIG. 3, the 2ME gave better results in all three methods relative to thecomparative DTDPA and TGA.

EXAMPLE 5

A sparged beaker (SB) test using 80/20 volume ratio brine/hydrocarbonwas conducted using 10 ppm of the mercaptoalcohol under 160° F. (71° C.)and 1 atm CO₂ saturation (101 mPa) for 20 hours. Both 2ME and1-mercapto-2-propanol (MP) demonstrated corrosion inhibition as seen inthe results plotted in FIG. 4. The 2MB gave 87.2% corrosion inhibitionand MP gave 86.0% inhibition.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof, and has been demonstrated aseffective in greatly improving corrosion inhibition in hydrocarbons.However, it will be evident that various modifications and changes canbe made thereto without departing from the broader spirit or scope ofthe invention as set forth in the appended claims. Accordingly, thespecification is to be regarded in an illustrative rather than arestrictive sense. For example, specific mercaptoalcohols, proportionsthereof, and combinations thereof, and specific hydrocarbons, other thanthose specifically tried, falling within the claimed parameters, but notspecifically identified or tried in a particular application to inhibitcorrosion, are within the scope of this invention.

We claim:
 1. A corrosion-inhibited fluid comprising a corrosioninhibitor composition comprising a water soluble mercaptoalcoholselected from the group consisting of mercaptoalcohols having theformula: (HS)_(n)—R—(OH)_(m)  where R is a straight, branched, cyclic orheterocyclic alkylene, hydrocarbon moiety having from 1 to 30 carbonatoms; n is from 1 to 3; m is 1; and the heteroatom in the heterocyclicmoiety substituent is selected from the group consisting of N, O, S andP and having the formula:

where R′ and R″ are independently selected from the group consisting ofH, straight, branched, cyclic or heterocyclic, alkyl, aryl, alkylaryland arylalkyl where the heteroatom in the heterocyclic moiety isselected from the group consisting of N, O, S and P, and where the totalnumber of carbon atoms in the mercaptoalcohol is from 1 to 8; and ahydrocarbon in contact with an iron-based alloy.
 2. The fluid of claim 1where R is a straight, branched, or cyclic alkylene, hydrocarbon moietyhaving from 1 to 8 carbon atoms; and n is
 1. 3. The fluid of claim 1where the mercaptoalcohol is selected from the group consisting of2-mercaptoethanol, 2-mercaptopropanol, 1-mercapto-2-propanol,2-mercaptobutanol, and mixtures thereof.
 4. The fluid of claim 1 wherethe mercaptoalcohol is the only corrosion inhibitor present in thecorrosion inhibitor composition.
 5. The fluid of claim 1 where theproportion of mercaptoalcohol in the corrosion inhibitor compositionranges from about 0.1 to about 70 wt. %.
 6. The fluid of claim 1 wherethe corrosion inhibitor composition further comprises a solvent selectedfrom the group consisting of water, alcohols, and aromatic compounds. 7.A corrosion-inhibited fluid comprising: a corrosion inhibitorcomposition comprising: from about 0.1 to about 70 wt. %, based on thetotal corrosion inhibiting composition, of a water solublemercaptoalcohol having the formula:

where R′ and R″ are independently selected from the group consisting ofH, straight, branched, cyclic or heterocyclic, alkyl, aryl, alkylaryland arylalkyl, where the heteroatom in the heterocyclic moiety isselected from the group consisting of N, O, S and P, and where the totalnumber of carbon atoms in the mercaptoalcohol is from 1 to 8; and asolvent selected from the group consisting of water, alcohols, andaromatic compounds; and a hydrocarbon in contact with an iron-basedalloy.
 8. The fluid of claim 1 where the hydrocarbon is a produced orprocessed hydrocarbon product from petroleum or natural gas.
 9. Acorrosion-inhibited fluid comprising a corrosion inhibitor compositioncomprising a water soluble mercaptoalcohol selected from the groupconsisting of mercaptoalcohols having the formula: (HS)_(n)—R—(OH)_(m) where R is a straight, branched, cyclic or heterocyclic alkylene,hydrocarbon moiety having from 1 to 30 carbon atoms; n is from 1 to 3; mis 1; and the heteroatom in the heterocyclic moiety substituent isselected from the group consisting of N, O, S and P and having theformula:

where R′ and R″ are independently selected from the group consisting ofH, straight, branched, cyclic or heterocyclic, alkyl, aryl, alkylaryland arylalkyl where the heteroatom in the heterocyclic moiety isselected from the group consisting of N, O, S and P, and where the totalnumber of carbon atoms in the mercaptoalcohol is from 1 to 8; and atleast one additional corrosion inhibitor selected from a group ofcorrosion inhibitors consisting of imidazolines, amides, amines,quaternary amines, phosphate esters, polycarboxylic acids, and mixturesthereof a hydrocarbon in contact with an iron-based alloy.
 10. The fluidof claim 9 where R is a straight, branched, or cyclic alkylene,hydrocarbon moiety having from 1 to 8 carbon atoms; n is 1 and maverages from 1 to
 3. 11. The fluid of claim 9 where the mercaptoalcoholis selected from the group consisting of 2-mercaptoethanol,2mercaptopropanol, 1-mercapto-2-propanol, 2-mercaptobutanol, andmixtures thereof.
 12. The fluid of claim 9 where the hydrocarbon is aproduced or processed hydrocarbon product from petroleum or natural gas.13. The fluid of claim 9 where the proportion of mercaptoalcohol in thecorrosion inhibitor composition ranges from about 0.1 to about 70 wt. %.14. The fluid of claim 9 where the corrosion inhibitor compositionfurther comprises a solvent selected from the group consisting of water,alcohols, and aromatic compounds.